The present invention relates to a circuit and process for controlling recharging of batteries and, more particularly, to a circuit and a process for obtaining fully charged batteries by interrupting the charging of the battery during a given time.
Generally, one widely used method for sensing the fully charged state of a battery during recharging relies upon detection of a minus delta voltage. One battery manufacturing company has recommended detection of a minus delta voltage only when recharging a battery at high speed because a minus delta voltage is not generated in most cases while supplying the battery with electrical charging current below 0.3 C. More specifically, a minus delta voltage is not generated while a battery is at a high temperature and, if the battery has not been used for a long time or if the battery is in a low-voltage state just after manufacture, a minus delta voltage phenomenon may be generated. Furthermore, with contemporary charging circuits, since the temperature of the battery as well as its voltage should be measured in order to sense the state of the charge carded by a battery, the production cost of such circuits is high. I have also found that when an electrical current is continuously supplied to a battery, waste heat can be radiated to other components in a circuit, thereby deleteriously influencing the performance of the circuit.
One recent effort described in U.S. Pat. No. 5,444,353 to S. Shinohara, et al., for a Battery Charger, depends upon an immediate application of an initial constant amplitude charging current to a battery prior to making an effort to determine the state of the battery. Other contemporary efforts, such as that found in U.S. Pat. No. 5,451,880 to Yamagishi, et al., for a Battery-Charging Circuit, endeavors to detect a complete charge as well as an abnormality in a battery without relying upon either minus delta voltage or temperature control systems, depends upon immediate application of a quick charge to nickel-cadium and to nickel-hydrogen type batteries, with the amplitude of the quick charging current being in the range of 0.5 C to 2.0 C. I have found that an immediate application of a charging current having an amplitude within the ranges required for attaining a quick charge, is not always wise when the possibility exists that the battery is either already fully charged or is abnormal.